The invention relates to a "fire-safe" valve structure which avoids dangerous pressure build-up in the valve chamber by establishing communication between the valve chamber and the flow passage through the valve when the environment in the valve chamber reaches a preselected temperature or a preselected pressure condition, and more specifically to a valve seat that provides communication between the valve chamber and the upstream flow passage in the event the environment within the valve chamber reaches a preselected condition as to temperature or pressure.
Valves in pipelines that carry petroleum products are susceptible to exposure to abnormally high temperatures in the event of a fire along the pipeline. It is essential to effective pipeline operation that the valve not be destroyed by such high temperatures. Oftentimes during a fire when the valve chamber is sealed off from the remainder of the valve in the closed or open condition of the valve the high temperatures create excessive pressure in the valve chamber. The result is the valve may be destroyed, most often, by a shearing of the bonnet bolts. Thus, it is highly desirable to provide an improved valve structure which can withstand abnormally high temperatures.
Heretofore, applicant is unaware of any valve or valve seat that provides a relief feature wherein the valve chamber is placed in communication with the flow passage through the valve when the environment within the valve chamber reaches a preselected temperature. While it has been known to provide valves with a by-pass between the chamber and flow passage at a preselected pressure differential, these conventionally employ check valves in the by-pass which lack reliability at high temperatures. They are also mounted externally of the valve in an exposed position.